This invention relates to communication systems and in particular to high frequency (HF) communications systems that utilize channel-parameter-measurement and link-quality-evaluation systems.
High frequency radio communications have traditionally been a medium to provide economical, long and short distance non-line-of-sight communications. However, there are problems associated with the use of high frequency communication systems. These include degradation of the communication links through jamming, both intentional and unintentional, atmospheric conditions, multipath propagation, and interferences. U.S. Pat. No. 4,328,581 provided an adaptive communication system which measured and stored an elementary assessment of the link quality according to the channel and address of a station transmitting the message so that when a transmission is initiated to the station the best available channel is selected and utilized for communications.
The above referenced patent determined the link quality based upon the measured signal-to-noise ratio, the estimated bit error rate for a specialized test signal, or whether or not the channel was available. Although these parameters are useful in evaluating the link quality of a communication link, it has been found that additional information is required to achieve an accurate prediction of the overall link performance, especially for high-speed data-transmission channel applications. This additional information includes an accurate measurement of frequency-selective fading, time selective fading, a noise and interference profile and other variables which can be converted into useful general HF channel parameters and a link quality assessment.